Antenna switching system with adaptive switching criteria

1. A method for using an electronic device that has at least two antennas of which one is selectively used to handle wireless communications traffic, comprising:

with the antennas, obtaining difference measurements reflecting how much received antenna signal strength differs between the antennas;

applying first and second filters with different filtering speeds to the difference measurements to produce respective first and second filtered difference measurements; and

applying antenna switching criteria to the first and second filtered difference measurements to determine whether to switch a first of the antennas into use in handling the wireless traffic in place of a second of the antennas.

2. The method defined in claim 1 wherein applying the antenna switching criteria comprises comparing at least the one of the filtered difference measurements to a threshold.

3. The method defined in claim 2 further comprising adjusting the threshold in real time.

4. The method defined in claim 3 wherein adjusting the threshold comprises adjusting the threshold in response to a computed variation between the first filtered difference measurements and the second filtered difference measurements.

5. The method defined in claim 4 further comprising:

gathering information on whether the electronic device is transitioning from a fast fading environment to a slow fading environment, wherein adjusting the threshold comprises adjusting the threshold in response to the gathered information.

6. The method defined in claim 5 wherein gathering the information comprises:

producing movement data with a satellite positioning system receiver.

7. The method defined in claim 5 wherein gathering the information comprises:

producing movement data with an accelerometer positioning system receiver.

8. The method defined in claim 1 wherein applying the antenna switching criteria comprises comparing the first filtered difference measurements to a first threshold and comparing the second filtered difference measurements to a second threshold that is different than the first threshold.

9. The method defined in claim 8 further comprising adjusting the second threshold in real time.

10. The method defined in claim 9 further comprising:

computing how much variation is exhibited between the first filtered difference measurements and the second filtered difference measurements.

11. The method defined in claim 10 wherein adjusting the second threshold comprises adjusting the second threshold in response to the computed variation.

12. A method of operating an electronic device that has first and second antennas, wherein one of the antennas is selectively switched into use to serve as a currently active antenna that handles wireless communications traffic for the electronic device, the method comprising:

measuring a first signal strength associated with receiving antenna signals through the first antenna;

measuring a second signal strength associated with receiving antenna signals through the second antenna;

producing difference measurements by computing differences between the first and second measured signal strengths;

applying a first averaging filter to the difference measurements to produce first filtered difference measurements;

applying a second averaging filter to the difference measurements to produce second filtered difference measurements; and

applying antenna switching criteria to the first and second filtered difference measurements to determine which of the antennas is to serve as the currently active antenna.

13. The method defined in claim 12 wherein applying the antenna switching criteria comprises comparing the first filtered difference measurements to a first threshold and comparing the second filtered difference measurements to a second threshold that is different than the first threshold.

14. The method defined in claim 13 further comprising adjusting the second threshold during operation of the electronic device.

15. The method defined in claim 14 wherein adjusting the second threshold comprises:

computing how much variation exists between the first filtered difference measurement and the second filtered difference measurement; and

lowering the second threshold in response to decreases in the computed variation.

16. The method defined in claim 15 wherein adjusting the second threshold comprises increasing the second threshold in response to determining that movement of the electronic device has slowed.

17. An electronic device, comprising:

wireless circuitry including at least first and second antennas and radio-frequency transceiver circuitry that is coupled to the first and second antennas; and

control circuitry configured to control the wireless circuitry to switch a selected one of the first and second antennas into use to handle wireless communications traffic for the electronic device, wherein the control circuitry and wireless circuitry are configured to:

obtain difference measurements reflecting how much received antenna signal strength differs between the antennas;

apply first and second time-based averaging filters with different respective filtering speeds to the difference measurements to produce respective first and second filtered difference measurements; and

apply antenna switching criteria to the first and second filtered difference measurements to determine whether to switch the first or the second antenna into use to handle the wireless communications traffic.

18. The electronic device defined in claim 17 wherein the antenna switching criteria comprise first and second thresholds and wherein the control circuitry and wireless circuitry are further configured to:

compare the first filtered difference measurements to the first threshold to determine whether to generate a first antenna switching request; and

compare the second filtered difference measurements to the second threshold to determine whether to generate a second antenna switching request.

19. The electronic device defined in claim 18 wherein the control circuitry and wireless circuitry are further configured to process the first and second antenna switching requests to determine whether to switch which of the first and second antennas is being used to handle the wireless communications traffic.

20. The electronic device defined in claim 18 wherein the control circuitry and wireless circuitry are further configured to adjust the second threshold in real time during operation of the electronic device in a wireless network.

21. A method of operating an electronic device that has first and second antennas, wherein one of the antennas is selectively switched into use to serve as a currently active antenna that handles wireless communications traffic for the electronic device, the method comprising:

measuring a first signal strength associated with receiving antenna signals through the first antenna;

measuring a second signal strength associated with receiving antenna signals through the second antenna;

producing difference measurements by computing differences between the first and second measured signal strengths;

applying first and second filters with different filtering speeds to the difference measurements to produce respective first and second filtered difference measurements; and

applying antenna switching criteria to the first and second filtered difference measurements to determine which of the antennas is to serve as the currently active antenna, wherein applying the antenna switching criteria comprises computing a value indicative of how many times per unit time an antenna switching threshold is exceeded by at least one of the first and second filtered difference measurements.

22. The method defined in claim 21 wherein the first and second filters comprise averaging filters, wherein applying the antenna switching criteria comprises comparing the value to a limit.

23. The method defined in claim 22 further comprising adjusting the limit in real time during operation of the electronic device in a wireless network.